/**
 * JDBM LICENSE v1.00
 *
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 2. Redistributions in binary form must reproduce the
 *    above copyright notice, this list of conditions and the
 *    following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. The name "JDBM" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of Cees de Groot.  For written permission,
 *    please contact cg@cdegroot.com.
 *
 * 4. Products derived from this Software may not be called "JDBM"
 *    nor may "JDBM" appear in their names without prior written
 *    permission of Cees de Groot. 
 *
 * 5. Due credit should be given to the JDBM Project
 *    (http://jdbm.sourceforge.net/).
 *
 * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
 * Contributions are Copyright (C) 2000 by their associated contributors.
 *
 * $Id: FreeLogicalRowIdPageManager.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
 */

package com.sunchangming.stmdb.recman;

import java.io.IOException;

/**
 * This class manages free Logical rowid pages and provides methods to free and
 * allocate Logical rowids on a high level.
 */
final class FreeLogicalRowIdPageManager {
	// our record file
	private final RecordFile file;
	// our page manager
	private final PageManager pageman;

	/**
	 * Creates a new instance using the indicated record file and page manager.
	 */
	FreeLogicalRowIdPageManager(RecordFile file, PageManager pageman) throws IOException {
		this.file = file;
		this.pageman = pageman;
	}

	/**
	 * Returns a free Logical rowid, or null if nothing was found.
	 */
	Location get() throws IOException {

		// Loop through the free Logical rowid list until we find
		// the first rowid.
		Location retval = null;
		final PageCursor curs = new PageCursor(pageman, Magic.FREELOGIDS_PAGE);
		while (curs.next() != 0) {
			final FreeLogicalRowIdPage fp = FreeLogicalRowIdPage
					.getFreeLogicalRowIdPageView(file.get(curs.getCurrent()));
			final int slot = fp.getFirstAllocated();
			if (slot != -1) {
				// got one!
				retval = new Location(fp.get(slot));
				fp.free(slot);
				if (fp.getCount() == 0) {
					// page became empty - free it
					file.release(curs.getCurrent(), false);
					pageman.free(Magic.FREELOGIDS_PAGE, curs.getCurrent());
				} else
					file.release(curs.getCurrent(), true);

				return retval;
			} else {
				// no luck, go to next page
				file.release(curs.getCurrent(), false);
			}
		}
		return null;
	}

	/**
	 * Puts the indicated rowid on the free list
	 */
	void put(Location rowid) throws IOException {

		PhysicalRowId free = null;
		final PageCursor curs = new PageCursor(pageman, Magic.FREELOGIDS_PAGE);
		long freePage = 0;
		while (curs.next() != 0) {
			freePage = curs.getCurrent();
			final BlockIo curBlock = file.get(freePage);
			final FreeLogicalRowIdPage fp = FreeLogicalRowIdPage.getFreeLogicalRowIdPageView(curBlock);
			final int slot = fp.getFirstFree();
			if (slot != -1) {
				free = fp.alloc(slot);
				break;
			}

			file.release(curBlock);
		}
		if (free == null) {
			// No more space on the free list, add a page.
			freePage = pageman.allocate(Magic.FREELOGIDS_PAGE);
			final BlockIo curBlock = file.get(freePage);
			final FreeLogicalRowIdPage fp = FreeLogicalRowIdPage.getFreeLogicalRowIdPageView(curBlock);
			free = fp.alloc(0);
		}
		free.setBlock(rowid.getBlock());
		free.setOffset(rowid.getOffset());
		file.release(freePage, true);
	}
}
